While the steel of both barrels is Chrome moly vanadium, the difference is how they are manufactured and finished.
The standard barrel has its lands and grooves formed by button broaching, and then the bore is chrome lined.
The hammer forged barrel has its lands and grooves beaten into shape around a tapered mandrel, and then the bore is chrome lined in a different process that allows for a much thicker chrome lining. This process was developed to produce a lining that would stand up to the abuse FN's machine gun barrels would have to endure.
The mandrel diameter would be larger than the button diameter to compensate for the increased thickness in chrome lining.
Accuracy out of either will depend more on the shooter.
Both are more accurate than I am